1. Field of the Invention
The present invention relates to an electrical part wherein a sliding member provided on an operating member of a rotary type or slide type is adapted to slide on a circuit pattern formed on an insulating film, and more particularly to a structure for holding the operating member and a structure for protecting the circuit pattern in such an electrical part.
2. Description of the Prior Art
In the electrical parts of the above mentioned type, a rotary variable resistor, for example, of the structure as shown in a cross-sectional view in FIG. 7 has so far been used. Referring to the drawing, 30 denotes an operating member on the operating side of the rotary type variable resistor and 31 denotes a circuit board on its circuit side. On the under surface of the operating member 30 is attached sliding members 32 by fusion and at the circumferential portion thereof is provided a protruded portion 30a. On the circuit board 31 is provided a circuit pattern 33.
The circuit pattern 33, as shown in its plan in FIG. 8, is formed of a resistor layer 34 on the inner side and a current collector layer 35 on the outer side, and the resistor layer 34 and the current collector layer 35 are connected with a desired circuit pattern (not shown) through lead terminals 34a and 35a, respectively. The sliding members 32 are adapted to slide on the resistor layer 34 and the current collector layer 35, while the under surface of the protruded portion 30a is adpated to slide on the circuit board 31 otside the circuit pattern 33, whereby a predetermined clearance is provided between the operating member 30 and the circuit board 31 and the sliding members 32 are thus adapted to slide on the circuit pattern 33 with a constant contact pressure maintained therebetween.
In the rotary type variable resistor structured as above, if the operating member 30 is roatated, the sliding members 32 are accordingly rotated on the circuit pattern 33 and a desired resistance value is thereby obtained through the lead terminals 34a and 35a. At this time, the under surface of the protruded portion 30a formed on the operating member 30 slides on the circuit board 31 outside the circuit pattern 33 as indicated by two-dot chain lines in FIG. 8 and thus crosses portions of the lead terminals 34a, 35a. Accordingly, there have been such disadvantages involved in the prior art electrical part that a great number of repeated rotations of the operating member 30 cause the protruded portion 30a to rub out the lead terminals 34a, 35a thereby leading to disconnection in the circuit pattern 33 and the same cause conductive particles from the leads 34a, 35a to deposit on the under surface of the protruded portion 30a thereby leading to a short circuit in the circuit pattern 33.
On the other hand, a slide type electrical part, in general, is used as a so-called discrete part being provided by incorporating a board on which a circuit pattern of a resistor layer, a current collector layer, and the like are formed and an operating member including a sliding member sliding on the circuit pattern into a frame body forming an external shell.
While a number of various electrical parts having different functions such as push switches and the like including the above slide type electrical parts are disposed according to the need on the front panel of a VTR, microwave oven, and other electronic apparatuses, these parts are usually arranged such that the discrete electrical parts which are partly exposed from the front panel are internally soldered to a printed circuit board at their terminals. Therefore, there has been such an advantage that such a control panel in a constructed state becomes considerably thick.
Therefore, to provide thinner one out of those discrete electrical parts particulary for the push switch, the so-called membrane switch has come to be used, which is formed of a pair of insulating films with upper and lower electrodes printed thereon laminated together with a spacer interposed therebetween. Though the appearance of the membrane switch has contributed to the provision of thinner electrical parts, the above described discrete parts have still been used for the slide type electrical parts, and therefore, the provision of a thinner control panel as a whole has not been sufficiently achieved.
The rotary type electrical part is generally used as a so-called discreter part being provided by incorporating a board, on which a circuit pattern of a resistor layer, current collector layer, and the like are formed, and an operating member including a sliding member sliding on the circuit pattern into a frame body forming an external shell.
While various electrical parts having different functions as push switches, rotary switches, rotary type variable resistors, and the like are provided on the front panel of a VTR, microwave oven, and other electronic apparatuses, these parts are arranged to provide a control panel such that these discrete parts which are partly exposed out of the front panel are internally soldered to a printed circuit board at their terminals. According to the recent tendency in designing toward thinner control panels of the above described type, and particularly for push switches out of the discrete electrical parts, a switch device called a membrane switch has come to be used, which membrane switch is formed of a pair of insulating films with electrodes printed thereon laminated together with a spacer interposed therebetween. As far as the rotary electrical parts are concerned, however, the above described discrete parts have still been used, and therefore, there has been some limit in providing a thinner control panel as a whole.